function volforce = int_f(xx,lambda,mu)
x=xx(1,1);
y=xx(1,2);
     volforce = zeros(size(x));
volforce(1,1) = -((lambda+2*mu)*(2+2/(x^2 + y^2 + 1) -...
               (4*x^2)/(x^2 + y^2 + 1)^2)+...
              (lambda+mu)*(-(4*x*y)/(x^2 + y^2 + 1)^2)+...
               mu*(2+2/(x^2 + y^2 + 1) - ...
               (4*y^2)/(x^2 + y^2 + 1)^2));
volforce(1,2) = -((lambda+2*mu)*(2+2/(x^2 + y^2 + 1) -...
               (4*y^2)/(x^2 + y^2 + 1)^2)+...
              (lambda+mu)*(-(4*x*y)/(x^2 + y^2 + 1)^2)+...
               mu*(2+2/(x^2 + y^2 + 1) - ...
               (4*x^2)/(x^2 + y^2 + 1)^2));           
   
       



